There is an increasing demand for alkylate fuel blending feedstock. As a fuel-blending component alkylate combines a low vapour pressure with high octane properties.
Almost all alkylate is produced by reacting isobutane with butene in the presence of a suitable acidic catalyst. The most used catalysts are HF and sulphuric acid, although other catalysts such a solid acid catalyst have been reported. Recently, the alkylation of isoparaffins with olefins using an acidic ionic liquid catalyst has attracted attention as an alternative to HF and sulphuric acid catalysed alkylation processes.
In for instance U.S. Pat. No. 7,285,698 a process for manufacturing an alkylate oil is disclosed, which uses a composite ionic liquid catalyst to react isobutane with a butene. In the process of U.S. Pat. No. 7,285,698, isobutane and butene are supplied to a reactor and the alkylate is formed by contacting the reactants with a composite ionic liquid under alkylation conditions. The reactor effluent is separated and the ionic liquid phase is recycled to the reactor while the hydrocarbon phase is treated to retrieve the alkylate.
In for instance Liu et al. (Z. Liu, R. Zhang, C. Xu, R. Xia, Ionic liquid alkylation process produces high-quality gasoline, Oil and Gas Journal, vol 104, Issue 40, 2006) it is mentioned that it is possible to retrofit a sulphuric acid alkylation unit for use of an IL catalyst. However, it is mentioned that it is necessary to modify the settler unit to improve the separation of the reactor effluent, i.e. the ionic liquid catalyst and hydrocarbon phase.
In US2005/0119423, a process for preparing polyalphaolefins is disclosed using an ionic liquid catalyst. In the process of US2005/0119423, the reactor effluent is provided to a separator to obtain a polyalphaolefin-containing phase, which still comprises remaining ionic liquid catalyst. It is suggested in US2005/0119423, to mix the polyalphaolefin-containing phase with water to deactivate the catalyst and subsequently separate the polyalphaolefin-containing phase from the water in two additional sequential separation steps.
There is a need in the art for an ionic liquid alkylation process, which provides an improved separation of the reactor effluent.